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Warm Airmass Intrusions (WAIs) from the mid‐latitudes significantly impact the Arctic water budget. Here, we combine water vapor isotope measurements from the MOSAiC expedition, with a Lagrangian‐based process attribution diagnostic to track moisture transformation in the central Arctic Ocean during two WAIs, under contrasting sea‐ice concentrations (SIC). During winter with high SIC, two moisture supplies are identified. The first is Arctic moisture, locally‐sourced over the sea ice, with isotopic composition influenced by kinetic fractionation during ice‐cloud formation and vapor deposition. This moisture is rapidly overprinted by low‐latitude moisture advected poleward during WAI. In summer under low SIC, moisture is supplied through evaporation from land and ocean, with moisture removal via liquid‐cloud and dew formation. The isotopic composition reflects the influence of higher relative humidity at the evaporation sites. Given the projected increase of frequency and duration of WAIs, our study contributes to assessing process changes in the Arctic water cycle. Plain Language Summary: The movement of warm and moist airmasses from lower latitudes has a big effect on the Arctic climate system. We used data from the MOSAiC drift expedition, where we measured the isotopic composition of water vapor. Water isotopes are powerful tracers of where moisture came from and how it changed during the transport. We focused on two specific warm air intrusions, occurring in February and September 2020 respectively, when the amount of sea ice was different. During the winter, the isotopic composition of the airmasses was primarily influenced by in‐Arctic moisture exchanges over sea ice. This local moisture was swiftly replaced by isotopically‐distinct warmer and moister airmasses coming from lower latitudes during the warm intrusion. In summer, when there was less sea ice, we found that water came mainly from ocean evaporation with additional land evaporation during the air intrusion. The isotopic composition of vapor was influenced by how humid the places it came from were. As warm air intrusions are expected to happen more often and last longer in the future, our study helps us understand how they affect the Arctic water cycle. Key Points: Transformation of moist airmasses and their isotopic composition during warm air intrusions depends on sea‐ice extentIn winter, warm air intrusions suppress ice‐cloud formation and kinetic isotopic fractionation over sea iceIn summer, d‐excess is driven by vapor pressure gradients between ocean skin layer and the lower atmosphere at the evaporative sites [ABSTRACT FROM AUTHOR]

Environmental context: Carbonaceous components in PM2.5 have a negative effect on the environment, human health and climate. We explored the pollution characteristic, potential sources and interaction of carbonous aerosols in two adjacent areas in Shanxi, China. The concentration levels of organic carbon and elemental carbon were of a moderate level of all those measured between 2009 and 2020. Vehicle exhaust and coal combustion were the two main sources, and Yuci may be affected by the regional transport of Taiyuan in winter. Rationale: Carbonaceous aerosols seriously affect people's health and have a strong scattering effect on visible light. Pollution cuased by carbonaceous components in Taiyuan is serious. Numerous universities in Taiyuan have been moving to Yuci college town since 2013, and the amount of organic pollutants has increased gradually with the growing population. It is necessary to study the characteristics and relationship of carbonaceous aerosols in these two adjacent areas. Methodology: PM2.5 samples were collected in Taiyuan and Yuci college town in 2017 and 2018, and eight carbonaceous components were analysed using a Sunset Laboratory analyser. Pollution characteristic, potential sources and interaction of carbonous aerosols in the two adjacent areas were investigated. Results: The average organic carbon (OC) and elemental carbon (EC) concentrations were 12.6 and 6.8 µg m−3 in Taiyuan and 11.7 and 6.9 µg m−3 in Yuci. The OC and EC concentrations in Taiyuan can be approximately divided into three levels between 2009 and 2020, and the OC and EC levels in Taiyuan studied here (2017 and 2018) were in the middle level. The OC and EC concentrations were higher when the temperature was lower. Discussion: The OC concentration in December was the highest among three winter periods, which may be caused by secondary organic carbon formation related to the lower temperature and an inversion layer. Four source categories were identified using positive matrix factorisation, namely secondary source (25.0%), dust source (16.6%), vehicle exhaust (27.0%) and coal combustion (31.4%). In Taiyuan and Yuci, the trajectory clusters were mainly from north-west and west in winter, whereas the air masses not only originated from north-west, but also north and south in autumn. Yuci may be affected by Taiyuan's regional transport in winter. The results clarify the characteristics of carbon aerosols in the two adjacent areas, and provide fundamental data for the prevention and control of regional air pollutants. Environmental context. Carbonaceous components in PM2.5 have a negative effect on the environment, human health and climate. We explored the pollution characteristic, potential sources and interaction of carbonous aerosols in two adjacent areas in Shanxi, China. The concentration levels of organic carbon and elemental carbon were of a moderate level of all those measured between 2009 and 2020. Vehicle exhaust and coal combustion were the two main sources, and Yuci may be affected by the regional transport of Taiyuan in winter. [ABSTRACT FROM AUTHOR]

The paper aims to analyse the relationship between the amount of global solar radiation (GSR) reaching the Earth’s surface in Poland and the direction of air mass advection, using 72-h backward trajectories (1986–2015). The study determined average daily sums of GSR related to groups of trajectories with certain similarities in shape. It was found that the average daily sums of GSR during air mass inflow from all the directions (clusters) identified were significantly different from the average daily sum in the multi-year period. A significant increase in the amount of GSR over Poland is accompanied by air mass inflow from the north and east. The frequency of these advection directions is 27% of all days. The western directions of advection prompt different GSR sums: from slightly increased during advection from the north-west, to significantly decreased during advection from the west (from the central and western part of the North Atlantic). Special attention was given to days with extremely large (above the 0.95 percentile) and with the largest (above the 0.99 percentile) GSR sums. These are prompted by two main types of synoptic conditions: the Azores High ridge covering Central and Southern Europe; and the high-pressure areas which appear in Northern and Central Europe.

The paper aims to analyse the relationship between the amount of global solar radiation (GSR) reaching the Earth's surface in Poland and the direction of air mass advection, using 72-h backward trajectories (1986–2015). The study determined average daily sums of GSR related to groups of trajectories with certain similarities in shape. It was found that the average daily sums of GSR during air mass inflow from all the directions (clusters) identified were significantly different from the average daily sum in the multi-year period. A significant increase in the amount of GSR over Poland is accompanied by air mass inflow from the north and east. The frequency of these advection directions is 27% of all days. The western directions of advection prompt different GSR sums: from slightly increased during advection from the north-west, to significantly decreased during advection from the west (from the central and western part of the North Atlantic). Special attention was given to days with extremely large (above the 0.95 percentile) and with the largest (above the 0.99 percentile) GSR sums. These are prompted by two main types of synoptic conditions: the Azores High ridge covering Central and Southern Europe; and the high-pressure areas which appear in Northern and Central Europe. [ABSTRACT FROM AUTHOR]

A series of lockdown measures in response to the Corona Virus Disease 2019 (COVID-19) outbreak resulted in a drop in anthropogenic emissions and changes in concentrations of PM2.5 and O3. Backward trajectories analysis, cluster analysis, potential source contribution function (PSCF) and concentration weighted trajectory (CWT) technologies were conducted to reveal the characteristics and potential source areas of pollutants in Beijing before the COVID-19 outbreak (BCO period), during the outbreak (COB period) and after the outbreak (ACO period), as well as the contemporaneous period in 2019 (CCO period), which is critical for exploring the efficient control measures and making policy. The results indicated that despite the significant reduction in anthropogenic emissions during the epidemic, the PM2.5 concentrations increased by 1.0% caused by unfavorable meteorological conditions. O3 concentrations increased by 174.8% compared to that during the BCO period due to the increased temperature and inappropriate precursor reduction ratios. A considerable decrease of NO3- in PM2.5 was observed under the influence of significant reductions in vehicle emissions during the lockdown. The cluster analysis revealed that short-range transport played a significant role in the accumulation of local PM2.5 pollution, while long-range northwest airflows contributed more to O3 accumulation, and weakened as the season changed. The PSCF and CWT analysis demonstrated that potential source areas of PM2.5 were mostly located in the central and southern Hebei, the southwestern Shandong in the CCO period, and expanded to central Inner Mongolia and northern Shanxi in the COB period. These areas were highly compatible with the high emission areas of the emission inventory statistics. After the outbreak, the source areas of O3 were centered in the Beijing-Tianjin-Hebei region and Shandong province, with a radial dispersion in all directions, while they were distributed in the central Mongolia and Inner Mongolia during the other periods.

Estimated larval backward trajectories of three Tuna species, namely, Atlantic Bluefin Tuna (Thunnus thynnus, Linnaeus, 1758), Bullet Tuna (Auxis Rochei, Risso, 1801) and Albacore Tuna (Thunnus alalunga, Bonnaterre, 1788) in the central Mediterranean Sea, were used to characterize their spawning habitats, and to assess the impact of changes due to the major environmental parameters (i.e., sea surface temperature and chlorophyll-a concentration) on larval development during their advection by surface currents. We assumed that the environmental variability experienced by larvae along their paths may have influenced their development, also affecting their survival. Our results showed that the Tuna larvae underwent an accelerated growth in favorable environmental conditions, impacting on the notochord development. In addition, further updated information on spawning and larval retention habitats of Atlantic Bluefin Tuna, Bullet and Albacore Tunas in the central Mediterranean Sea were delivered. [ABSTRACT FROM AUTHOR]

Aerosol optical depth (AOD) measurements for 2017–2020 in urban Hohhot of the Mongolian plateau, a transition zone between the depopulated zone and East Asian urban agglomeration, were analyzed for the first time. Results show that annual AOD500 and Ångström exponent α440-675 were 0.36 ± 0.09 and 1.11 ± 0.16 (2017), 0.41 ± 0.12 and 0.90 ± 0.28 (2018), 0.38 ± 0.09 and 1.13 ± 0.24 (2019), 0.38 ± 0.12 and 1.17 ± 0.22 (2020), respectively, representing a slightly polluted level with a mixed type of coarse dust aerosol and a fine urban/industrial aerosol. Throughout the year, depopulated-zone continental air flows predominated in Hohhot (i.e., NW-quadrant wind), accounting for 82.12% (spring), 74.54% (summer), 63.61% (autumn), and 100% (winter). The clean and strong NW-quadrant air flows induced by the south movement of a Siberian anticyclone resulted in a low 500-nm AOD of 0.30 ± 0.29, 0.20 ± 0.15, 0.24 ± 0.29, and 0.13 ± 0.08 from spring to winter. Meanwhile, the local emissions from Hohhot city, as well as anthropogenic urban/industrial aerosols transported by southern and western air masses, originating from southern urban agglomeration and western industrial cities (Baotou, Wuhai, etc.), contributed to the highest aerosol loading, with significant transformation rates of the secondary aerosols Sulfate-Nitrate-Ammonium (SNA) of 47.45%, 57.39%, 49.88%, and 45.16–47.36% in PM2.5 for each season. The extinction fraction of fine aerosols under these anthropogenic trajectories can be as high as 80%, and the largest fine aerosol size was around 0.2–0.25 μm. Dust aerosols were suspending in urban Hohhot all year, although at different levels for different seasons, and the extinction fraction of dust aerosol during sandstorms was generally higher than 70%. [ABSTRACT FROM AUTHOR]

Residual levels and temporal–spatial distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) in dustfall were studied at the seasonal scale between June 2010 and May 2011 in the fifth largest shallow lake in China. PAHs flux of atmospheric deposition and the impact on the PAHs in the lake water column were estimated. The major sources of PAHs were identified by multiple methods. We found that (1) the seasonal residual levels of 16 priority controlled PAHs (PAH16) were spring (8.89 ± 3.93 μg g−1) > summer (6.68 ± 4.31 μg g−1) > winter (6.06 ± 2.95 μg g−1) > autumn (3.55 ± 2.21 μg g−1). (2) Significant positive correlations were found between the PAH levels in the dustfall and the suspended particle material (SPM) content, as well as between the deposition flux and the PAH content in the water in all four seasons. (3) Vehicle emissions, coal combustion, biomass combustion, and coke ovens were the four major sources in Lake Chaohu, accounting for 12.7%, 40.9%, 14.5%, and 31.9% of the total PAHs, respectively. (4) Compared to long-distance trajectories, short-distance trajectories played a more important role in the external sources of atmospheric PAHs in the region of Lake Chaohu. [ABSTRACT FROM AUTHOR]

The daily cycle of pollen concentrations reflects its genetic response to environmental conditions. The detailed study of these cycles was used to identify the influence of external sources on local pollen levels. In this work, three different daily profiles (Ci) of Olea pollen concentrations were identified in the city of Alicante (southeastern Spain) using cluster analysis. For this, 2-h data from 2010 to 2015 were used. The percentage frequency, pollen index and mean Olea pollen concentration (in pollen grains∙m−3) for each cluster were: C1 (∼91%, 8797, 26), C2 (∼7%, 4641,179) and C3 (∼2%, 1845, 308). C1 was the predominant pattern throughout the whole MPS, while C2 and C3 were only present in the middle of the MPS. Small variations in pollen concentrations throughout the day were observed for C1, while C2 and C3 showed the highest pollen concentration at ∼04:00 UTC and 10:00 UTC, respectively. C1 represented concentration patterns due to local pollen inputs, being influenced by precipitation events, sea breezes and the recirculation of air pollutants. On the other hand, C2 and C3 were strongly influenced by external pollen inputs from southwestern regions of Spain. The results of this study indicate that external inputs from these regions were associated with exposure of the population to high pollen concentrations for short periods of time. In contrast, inputs from the northwest were associated with exposure to lower pollen concentrations for longer periods of time. • Medium-range Olea pollen transport mask the influence of atmospheric events characteristic of the Mediterranean area. • Medium-range Olea pollen transport was observed before sunrise and in the afternoon. • "Hourly Olea pollen exposure" levels were estimated for the first time. [ABSTRACT FROM AUTHOR]

Abstract The atmospheric water cycle is a key component of the global energy and moisture exchange. In order to gain better understanding of the atmospheric processes and temporal variability and trends affecting precipitation in Crimea, we use a Lagrangian moisture source detection technique based on reanalysis data from the European Center for Medium‐Range Weather Forecasts. The study presents a quantitative picture of the major moisture sources that feed precipitation on the Crimean peninsula from February 1979 to January 2017. In total 51.3% of moisture stems from marine sources. Specifically, the main individual contributors are the Mediterranean Sea (15.3%), the Black Sea (14.4%), and the North Atlantic Ocean (13.9%). Continental moisture recycling contributes additional 46.9%. The amounts of moisture contribution from marine and continental sources and their respective moisture transport pathways are subject to strong seasonality. Winter precipitation in Crimea is predominantly sourced by the Mediterranean Sea. Long‐term temporal trends in contribution from any of the major moisture sources are absent during the study period. Statistically significant negative correlation between the North Atlantic Oscillation (NAO) index and contribution from moisture sources exists in winter for the Mediterranean (R = −0.22) and Black Seas (R = −0.23), and for the southern continental moisture source (R = −0.37). The North Atlantic Ocean moisture source exhibits a statistically significant positive correlation with NAO index during spring (R = 0.32).

The atmospheric water cycle is a key component of the global energy and moisture exchange. In order to gain better understanding of the atmospheric processes and temporal variability and trends affecting precipitation in Crimea, we use a Lagrangian moisture source detection technique based on reanalysis data from the European Center for Medium‐Range Weather Forecasts. The study presents a quantitative picture of the major moisture sources that feed precipitation on the Crimean peninsula from February 1979 to January 2017. In total 51.3% of moisture stems from marine sources. Specifically, the main individual contributors are the Mediterranean Sea (15.3%), the Black Sea (14.4%), and the North Atlantic Ocean (13.9%). Continental moisture recycling contributes additional 46.9%. The amounts of moisture contribution from marine and continental sources and their respective moisture transport pathways are subject to strong seasonality. Winter precipitation in Crimea is predominantly sourced by the Mediterranean Sea. Long‐term temporal trends in contribution from any of the major moisture sources are absent during the study period. Statistically significant negative correlation between the North Atlantic Oscillation (NAO) index and contribution from moisture sources exists in winter for the Mediterranean (R = −0.22) and Black Seas (R = −0.23), and for the southern continental moisture source (R = −0.37). The North Atlantic Ocean moisture source exhibits a statistically significant positive correlation with NAO index during spring (R = 0.32). Plain Language Summary: The atmospheric water cycle is a component of the global water cycle. It describes the behavior of water in the atmosphere from the evaporation in the source region to the final precipitation. This study presents a comprehensive picture of the precipitation water sources for the Crimean peninsula from 1979 to 2017. Additionally, trajectories allow to estimate travel times and pathways of air parcels. Approximately half of the Crimean precipitation originates in the marine sources: the Mediterranean Sea, Black Sea, and the North Atlantic Ocean. The other half derives from moisture recycling on the continent. Contributions from different sources vary seasonally. Despite considerable variability, there are no apparent long‐term trends in contributions from any precipitation source over the 38 years period. Sources are sensitive to the North Atlantic Oscillation index, particularly during winter. Key Points: Sources of precipitation for the Crimean peninsula in the Black Sea were identified using a Lagrangian approachThe main moisture sources are Mediterranean Sea, Black Sea, and Atlantic Ocean, as well as the continental landmass via moisture recyclingVariability in winter is partly related to the North Atlantic Oscillation. No significant temporal trends were detected over the study period [ABSTRACT FROM AUTHOR]

Despite frequent observations of high particulate matter (PM) concentrations in Seoul, Korea, the sulfate (SO42−) concentrations in PM with an aerodynamic diameter below or equal to 2.5 μm (PM2.5) in Seoul have been reduced during the 1990s. However, there has been no decreasing trend during the 2000s. Despite the very low ambient SO2 concentrations, high SO42− concentration episodes frequently occur in Seoul; however, the reasons for this remain poorly understood. In the present study, we sought to determine the major factors that enhance sulfur oxidation in Seoul by analyzing measurement data from an intensive air quality monitoring station in the Seoul metropolitan area acquired in 2015. Additionally, we aimed to distinguish the contributions of local sources and long-range transport to the elevated SO42− concentrations in PM2.5 in Seoul. In some cases in March and October 2015, the molar ratio of SO42− to SO2, which reflects sulfur partitioning between the particle and gas phases, showed an exponential increase with an increase of relative humidity (RH). However, despite the fact that the RH was high during August 2015, no statistically significant relationship was observed between RH and the molar ratio of SO42− to SO2 during this month. In August 2015, the molar ratio of SO42− to SO2 showed an exponential increase with increasing O3 concentration. Therefore, under sufficient RH, the concentrations of radical oxidants might be the most important factor that underlies the increase in ambient SO42− concentrations. No significant relationship was observed between the molar ratio of SO42− to SO2 and O3 in October. Furthermore, using Potential Source Density Function (PSDF) and backward trajectory analysis, the high SO42− concentrations in March 2015 were found to be caused by the transportation of air pollutants from China and local sources around Seoul. The high SO42− concentrations in August 2015 are concluded to have been greatly affected by these power plant emissions in the Taean area on the west coast of Korea. The high SO42− concentrations in October 2015 appear to have been caused by the transportation of air pollutants from North Korea. In summary, the high SO42− concentration in Seoul is affected by long-range transport from China and by the emissions from around the Seoul metropolitan area, such as Taean or North Korea. [ABSTRACT FROM AUTHOR]

This study analyzed the spatio-temporal variability of air quality data for six standard air pollutants (Particulate Matter 2.5 (PM2.5), Particulate Matter 10 (PM10), SO2, NO2, CO, and O3) in the Sichuan Basin (SCB), China from 2015 to 2018 in relation to the formation of haze using conventional meteorological data (temperature, wind speed, and relative humidity), satellite data (fire point data, vertical profiles of aerosol subtypes, and aerosol optical depth), planetary boundary layer height, and backward trajectories. The results indicated that the spatio-temporal evolution of the air quality index (AQI) had notable seasonality for the pollution severity in descending order: winter, spring, summer, and autumn. Autumn and winter severe haze events occurred in November and January, respectively, and were caused by higher local pollution emissions under stagnant air conditions. Spring severe haze events occurred in May and were caused by dust from Northwest China and local regions. Severe summer haze events occurred in July and were caused by local burning. Therefore, the analyses showed that local burning, stagnant meteorological conditions, air mass transport and anthropogenic pollution emissions played a key role in haze in the SCB. This study provides scientific insights for fully analyzing heavy air pollution in SCB, China, and also provides a scientific basis for pollution research in regions of complex terrain as basins and mountains. [ABSTRACT FROM AUTHOR]

Humic-like substances (HULIS), the most ubiquitous class of water-soluble organic compounds in the atmosphere could enhance the generation of reactive oxygen species (ROS), and play a significant role in impacting aerosol chemistry and health effects. In this study, twenty-three PM2.5 samples were collected in the atmosphere of suburban Shanghai from November 29 to December 17, 2015, and March 17 to April 30, 2016, during haze and non-haze days. The mean concentrations of HULIS in spring both in haze and non-haze days (2.34 ± 0.70 µg/m3 and 1.94 ± 0.88 µg/m3) were relatively higher than in that of winter (1.93 ± 0.95 µg/m3 and 1.31 ± 0.28 µg/m3). The ammonium, sulfate, and nitrate are the dominant ionic species in both winter and spring during haze days in suburban Shanghai. Correlation results revealed that HULIS formation was highly associated with the biomass burning (K) and secondary aerosols formation (SIA: NH4+, SO42−, NO3−) and also well-correlated with F− and ca.2+ ions, crustal elements (Al and Fe) and anthropogenic pollution metals (As, Se, Rb, Sr, and Pb), suggesting that HULIS-C formation might be from biomass burning and secondary aerosol processes and also mixed formation (marine, crustal and industrial emissions) sources. From the coinciding results of the clustering analysis and weighted-CWT model, the principal potential source regions were the short transports from the Yangtze River Delta (YRD) regions, local regions, marine areas (the Bohai Sea, the Yellow Sea, the East China Sea) and also the long-range transports from northwestern in those seasons. [ABSTRACT FROM AUTHOR]

The El Niño phase of the El Niño Southern Oscillation (ENSO) is typically associated with below‐average cool‐season rainfall in southeastern Australia (SEA). However, there is also large case‐to‐case variability on monthly time‐scales. Despite recent progress in understanding the links between remote climate drivers and this variability, the underlying dynamical processes are not fully understood. This reanalysis‐based study aims to advance the dynamical understanding by quantifying the contribution of midlatitude weather systems to monthly precipitation anomalies over SEA during the austral winter–spring season. A k‐means clustering reveals four rainfall anomaly patterns with above‐average rainfall (Cluster 1), below‐average rainfall (Cluster 2), above‐average rainfall along the East Coast (Cluster 3) and along the South Coast (Cluster 4). Cluster 2 occurs most frequently during El Niño, which highlights the general suppression of SEA rainfall during these events. However, the remaining three clusters with local above‐average rainfall are found in ∼52% of all El Niño months. Changes of weather system frequency determine the respective rainfall anomaly pattern. Results indicate significantly more cut‐off lows and warm conveyor belts (WCBs) over SEA in El Niño Cluster 1 and significantly fewer in El Niño Cluster 2. In El Niño Cluster 3, enhanced blocking south of Australia favours cut‐off lows leading to increased rainfall along the East Coast. Positive rainfall anomalies along the South Coast in El Niño Cluster 4 are associated with frontal rainfall due to an equatorward shift of the midlatitude storm track. Most of the rainfall is produced by WCBs and cut‐off lows but the contributions strongly vary between the clusters. In all clusters, rainfall anomalies result from changes in rainfall frequency more than in rainfall intensity. Backward trajectories of WCB and cut‐off low rainfall highlight the importance of moist air masses from the Coral Sea and the northwest coast of Australia during wet months. [ABSTRACT FROM AUTHOR]

To better understand the characteristics and sources of water soluble ions (WSI) in North China Plain (NCP), fine particles (PM 2.5) were simultaneously sampled at the summit (SM) and foot (FT) of Mount Tai during May 12th to June 24th, 2017. Ion chromatography analysis showed that concentration of WSI was lower at SM (22.26 ± 16.53 μg/m3) than that at FT (31.02 ± 21.92 μg/m3). The concentration and proportion of SO 4 2− in total WSI were both lower than the values reported in previous studies. Daytime WSI concentrations were higher than that at nighttime at SM, while the opposite results were obtained at FT, possibly associated with more anthropogenic activities and higher boundary layer height (BLH) during daytimes. A severe pollution event occurred during June 14th – June 16th was documented at both FT and SM. Regional transport and topography-forced vertical transport along the slope of the mountain could explain the higher concentrations of pollutants at SM. The analyses also indicated that NH 4 + existed mainly in the form of NH 4 HSO 4 and NH 4 NO 3 , but (NH 4) 2 SO 4 could also exist, especially when emissions of NH 4 + and NH 3 were increased during daytime at FT. The results of principal component analysis (PCA) illustrated that secondary aerosols, coal/biomass burnings, sea-salts and crustal/soil dusts were the main sources at SM, and secondary aerosols and crustal/soil dusts contributed most at FT. Backward air-mass trajectories were classified into four clusters, of which air masses with the highest frequency and WSI concentrations were originated from the southwest with secondary ions (SO 4 2-, NO 3 - and NH 4 +) as major pollutants. Image 1 [ABSTRACT FROM AUTHOR]

This paper studied the chemical characteristics and seasonal changes of PM2.5 in plateau cities on the southwest border of China. Urban air was sampled in Baoshan City during the rainy and dry seasons. Finally, 174 PM2.5 filters were collected (including 87 quartz and 87 Teflon samples for PM2.5). The mass concentrations, water-soluble inorganic ions, organic and inorganic carbon concentrations, and inorganic elements constituting PM2.5 were determined. Positive definite matrix factorization was used to identify potential sources of PM2.5, and the backward trajectory model was used to calculate the contribution of the long-distance transmission of air particles to the Baoshan area. It was found that in the wet season, most of the air masses come from the Indian Ocean and Myanmar. In the dry season, the air mass mainly comes from the China and Myanmar border area. The average concentration of PM2.5 in the wet and dry seasons was 23.17 ± 12.23 μg/m3. The daily mean value of OC/EC indicated that the measured SOC content was generated by the photochemical processes active during the sampling days. However, elements from anthropogenic sources (Na, Mg, Al, Si, P, K, Ca, Ti, Fe, Cu, Zn, Sb, Ba, and Pb) accounted for 99.51% and 99.40% of the total inorganic elements in the wet season and dry season, respectively. Finally, source apportionment showed that SIA, dust, industry, biomass burning, motor vehicle emissions, and copper smelting emissions constituted the major contributions of PM2.5 in Baoshan. Using combined data from three measurement sites provides a focus on the common sources affecting all locations.

In this work we use chemical fingerprints as characteristics ratios of specific crustal elements Ca/Al, Fe/Al, K/Al, Mg/Al, Mn/Al, Ca/Fe, and Mg/Fe to investigate the long-range transport of volcanic aerosols from Iceland. Volcanic dust enters the atmosphere during suspension processes from Icelandic deserts, but mainly from the dust hot spots in remote areas in Iceland, and it is transmitted to the central Balkan area (Belgrade). For this purpose, backward trajectories from Belgrade (φ = 44°48′; λ = 20°28′) in 2012 and 2013, simultaneous with atmospheric aerosols measurements, were calculated by using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. We found that about 17% of air masses passed over Icelandic territory and arrived to Balkan area. In almost all of these episodes ratios of some investigated elements in suburban aerosols of Balkan area corresponded to the ratios of elements investigated in surface soil of the Rangárvellir area – South Iceland in the vicinity of volcanoes. We identified several episodes, such as August 6–8, 2012; June 2–6, 2013; June 26–28, 2013; and September 18–20, 2013; with the characteristic ratios of the highest number of investigated elements in atmospheric aerosol of central Balkan corresponding to ratios from Icelandic soil material. This study provides evidence that Icelandic dust can travel long distances showing the importance of High Latitude Dust sources.

• Rainfall isotopic signature dependence with air temperature and rainfall amount. • Development of a Local Meteoric Water Line for Vallcebre Research Catchments, Spain • Use of backward trajectories relating moisture source and isotopic signature. • Case studies analysis of moisture origin and intra-event isotopic variability. This study investigates moisture origin, characteristics and intra-event scale variability of the isotopic signature of rainfall in a Mediterranean mountain area, based on data from the Vallcebre Research Catchments, NE Spain. Weekly data and samples were used to analyse the general dynamics of the isotopic composition of precipitation and its relationship with meteorological variables at the sampling site. Then, based on the data and samples available at the intra-event scale, the variability of the isotopic signature during rainfall events was characterised and an explanation of what caused the observed variability was attempted. Results at the weekly time scale show that the maximum relative deviation of the heavy isotopic content with respect to Standard Mean Ocean Water (δ 18 O) of the precipitation signature occurred during summer months and, in contrast, the minimum during winter months. The intra-annual trend of rainfall δ 18 O roughly followed the mean monthly air temperature. Using intra-event information, three main types of δ 18 O isotopic trends were found during rainfall events: most of the events had a V-shaped isotopic trend, followed by L-shaped and constant trend events. Changes in moisture sources 'diagnosed using a Lagrangian approach and a previously existing contribution algorithm' were one of the causes of the isotopic variability and changes at the intra-event scale, but these may also have been influenced by sub-cloud processes that modified the isotopic signature. Moisture sources for analysed events showed the main influence of the Mediterranean area, but also an important influence of the Atlantic Basin. [ABSTRACT FROM AUTHOR]

In order to investigate the seasonal variations in the chemical characteristics of PM2.5 at the plateau slope of a mountain city in southwest China, 178 PM2.5 filters (89 quartz and 89 Teflon samples for PM2.5) were collected to sample the urban air of Wenshan in spring and autumn 2016 at three sites. The mass concentrations, water-soluble inorganic ions, organic and inorganic carbon concentrations, and inorganic elements constituting PM2.5 were determined, principal component analysis was used to identify potential sources of PM2.5, and the backward trajectory model was used to calculate the contribution of the long-distance transmission of air particles to the Wenshan area. The average concentration of PM2.5 in spring and autumn was 44.85 ± 10.99 μg/m3. Secondary inorganic aerosols contributed 21.82% and 16.50% of the total PM2.5 in spring and autumn, respectively. The daily mean value of OC/EC indicated that the measured SOC content was generated by the photochemical processes active during the sampling days. However, elements from anthropogenic sources (Ti, Si, Ca, Fe, Al, K, Mg, Na, Sb, Zn, P, Pb, Mn, As and Cu) accounted for 99.38% and 99.24% of the total inorganic elements in spring and autumn, respectively. Finally, source apportionment showed that SIA, dust, industry, biomass burning, motor vehicle emissions and copper smelting emissions constituted the major components in Wenshan. This study is the first to investigate the chemical characterizations and sources of PM2.5 in Wenshan, and it provides effective support for local governments formulating air pollution control policies.

Size-fractionated particulate mercury (PHg) measurements were performed from November 2017 to January 2018 at Terra Nova Bay (Antarctica) for the first time. Samples were collected every 10 days by a six-stage high-volume cascade impactor with size classes between 10 μm and 0.49 μm. Total PHg concentrations were maxima (87 ± 8 pg m−3) in November, then decreased to values ~40% lower and remained almost constant until the end of the sampling period (~30 pg m−3). The trimodal aerosol mass distribution reveals that from 30% to 90% of the total PHg came in the size > 1.0 μm. Hg in the two coarse fractions was probably produced by the adsorption of oxidized Hg species transported by air masses from the Antarctic plateau or produced locally by sea ice edges. PHg in accumulation mode seemed to be related to gas–particle partitioning with sea salt aerosol. Finally, average dry deposition fluxes of PHg were calculated to be 0.36 ± 0.21 ng m−2 d−1 in the accumulation mode, 47 ± 44 ng m−2 d−1 in the first coarse mode, and 37 ± 31 ng m−2 d−1 in the second coarse mode. The present work contributed to the comprehension of the Hg biogeochemical cycle, but further research studies are needed.

Quantification of suspended particulate matter (SPM) measurements—together with statistical tools, polar contour maps and backward air mass trajectory analyses—were implemented to better understand the main local and remote sources of contamination in this pristine region. Field campaigns were carried out during the austral summer of 2016–2017 at the “Gabriel de Castilla” Spanish Antarctic Research Station, located on Deception Island (South Shetland Islands, Antarctic). Aerosols were deposited in an air filter through a low-volume sampler and chemically analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). Elements such as Al, Ca, Fe, K, Mg, Na, P, S, Cu, Pb, Sr, Ti, Zn, Hf, Zr, V, As, Ti, Mn, Sn and Cr were identified. The statistical tools together with their correlations (Sr/Na, Al/Ti, Al/Mn, Al/Sr, Al/Pb, K/P) suggest a potentially significant role of terrestrial inputs for Al, Ti, Mn, Sr and Pb; marine environments for Sr and Na; and biological inputs for K and P. Polar contour graphical maps allowed reproducing wind maps, revealing the biological local distribution of K and P (penguin colony). Additionally, backward trajectory analysis confirmed previous affirmations and atmospheric air masses following the Antarctic circumpolar pattern.

W pracy zaprezentowano metodę rozpoznawania odległych źródeł emisji pyłu drobnego PM2.5, polegającą na przestrzennej analizie łącznej informacji o imisji PM2.5 oraz o wstecznych trajektoriach mas powietrza, obliczonych za pomocą modelu HYSPLIT. Trajektorie wsteczne obliczono startując z wysokości 30, 50, 100 i 150 m n.p.g., dla trzech lokalizacji stacji pomiarowych stężeń PM2.5 (Diabla Góra, Gdańsk, Katowice), reprezentujących różne warunki środowiskowe. Wszystkim punktom pojedynczej trajektorii wstecznej przyporządkowano stężenie PM2.5 odpowiadające dacie startu obliczeń tej trajektorii. Użyto dobowych średnich stężeń PM2.5, a w przypadku Gdańska dodatkowo także godzinnych średnich, co umożliwiło ocenę skuteczności przedstawionej metody. Położenie odległych źródeł emisji pyłu drobnego zostało określone poprzez interpolację danych punktowych trajektorii do regularnej siatki przy zastosowaniu metody metryki danych. Każdemu węzłowi siatki przypisano wartość średnią obliczoną ze stężeń PM2.5 przyporządkowanych punktom trajektorii znajdujących się w obrębie tzw. elipsy wyszukiwania. Przed obliczeniem wartości średniej ukryto część danych, eliminując w ten sposób bliskie źródła emisji pyłu drobnego. Analizy objęły okres styczeń-marzec 2010 roku. Wyniki wskazały na odmienne pochodzenie mas powietrza w północnej i południowej Polsce. W Diablej Górze i Gdańsku odległe źródła emisji pyłu drobnego rozpoznano głównie w Białorusi i Rosji. W Katowicach również zaznaczył się wpływ źródeł białoruskich, ale jako najbardziej istotne odległe źródła emisji PM2.5 uznano te zlokalizowane na obszarze Rumunii, Węgier, Słowacji i Ukrainy.

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Dust storms (DS) are considered a common environmental phenomenon in numerous countries of the world, especially in the arid and semi-arid regions. DS causes a significant impact on human health, climate, the environment and many associated socioeconomic factors. The main goal of this study is to assess the sources of DS in the State of Kuwait. The present study investigates DS over Kuwait using the backward trajectories' simulation with MODIS satellite observations at various latitudes (1000, 3000, 5000 m) during the four seasons; winter, spring, summer, and fall. The trajectories' simulation was modeled using the HYSPLIT model to create the seasonal climatologic of air parcel trajectories. The meteorological data (e.g., visibility, wind speed, wind direction, temperature, and humidity) were collected during a 12-year period from 2000 to 2012. Daily trajectories were computed backward for five days from a central origin at several altitudes above the ground surface. The variability of the DS was analyzed daily, monthly, seasonally and annually. A case study on 25 March 2011 and two cases from each season were selected for analysis. The results showed that the HYSPLIT model was consistent with the MODIS satellite images. The sources of DS were identified from both the Sahara Desert and the Arabian Desert. Furthermore, there is a significant influence of the atmospheric conditions on the DS sources. The most influential parameter was visibility, from the west and the northwest direction. The present work provides evidence and suggestions for the origins of DS and is expected to help in establishing guidelines for public protection against dust particles and provides significant information to the concerned officials to take proper actions. [ABSTRACT FROM AUTHOR]

In the present study, surface ozone (O3), nitrogen oxides (NOx), and carbon monoxide (CO) levels were measured at two sites downwind of fire active region in the Indo-Gangetic Plain (IGP): Agra (27.16° N, 78.08° E) and Delhi (28.37° N, 77.12° E) to study the impact of post-harvest crop-residue fires. The study period was classified into two groups: Pre-harvest period and Post-harvest period. During the post-harvest period, an enhancement of 17.3 and 31.7 ppb in hourly averaged O3 mixing ratios was observed at Agra and Delhi, respectively, under similar meteorological conditions. The rate of change of O3 was also higher in the post-harvest period by 56.2% in Agra and 39.5% in Delhi. Relatively higher O3 episodic days were observed in the post-harvest period. Fire hotspots detected by Moderate Resolution Imaging Spectroradiometer (MODIS) along with backward air-mass trajectory analysis suggested that the enhanced O3 and CO levels at the study sites during the post-harvest period could be attributed to crop-residue burning over the North-West IGP (NW-IGP). Satellite observations of surface CO mixing ratios and tropospheric formaldehyde (HCHO) column also showed higher levels during the post-harvest period.Graphical abstract [ABSTRACT FROM AUTHOR]

The Mediterranean basin is indicated as a hot spot of climate change, which is an area whose climate is especially responsive to variations. The insular environment is one of the most threatened by the current climate change, especially in terms of drought events, with serious consequences for water scarcity and water stress. This issue is even enhanced in small islands, whose ecosystems are among more sensitive to climatic changes and water availability. The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in precipitation is globally recognized as a powerful natural tracer in the water cycle and represents the starting point to investigate hydrological processes. The understanding of the prevailing factors that drive the isotopic variability of precipitation in the Mediterranean is therefore essential to unravel the hydrological processes and to ensure proper and sustainable management of potentially vulnerable resources to climate change. Here, we discuss the results of multi-year isotopic monitoring in the period 2014–2021 of monthly precipitation collected on Pianosa Island (Italy), a small island located in the northern Tyrrhenian (western Mediterranean). The lower slope and intercept of the Local Meteoric Water Line of the island compared to the Global Meteoric Water Line indicated warmer and drier climatic conditions, suggesting the existence of sub-cloud evaporation processes of raindrops during precipitation, especially in summer. The mean δ18O of precipitation was lower with respect to other sites placed at higher elevation in this Mediterranean region, due to the lack of summer precipitation which were generally enriched in heavy isotopes. Temperature and amount effects may explain part of the δ18O variability observed at the monthly and seasonal scale. An HYSPLIT-based moisture uptake analysis indicated the area between the western Mediterranean basin, Italy, and the Adriatic Sea as the region that supplied most of the humidity associated with monthly precipitation samples on Pianosa Island. Less moisture was picked from the northwestern areas of Europe, the North Atlantic Ocean, the proximal Atlantic Ocean, the Iberian Peninsula and North Africa. Consistently with the rainout effect, the higher the moisture fraction picked from the more proximal regions, the more positive the δ18O of precipitation occurring on Pianosa Island; conversely, the higher the percentage of moisture sourced from more distal regions, the more negative the δ18O. A multiple linear model was proposed to predict the δ18O of monthly precipitation from temperature, precipitation amount and moisture origin data, which explained 45% of the δ18O variability. The deuterium excess variability on the island was partly controlled by the local climatic variables, whose effect potentially modifies the original d-excess signature imprinted at the moisture source. No relationship was found between the precipitation deuterium excess and moisture sources, suggesting that more attention should be paid when using the deuterium excess as a tracer of moisture origin, especially in the Mediterranean. • Multi-year isotopic monitoring of monthly precipitation on Pianosa Island (Italy) • Sub-cloud evaporation processes of raindrops may occur during precipitation • Temperature, precipitation and moisture origin data explain 45% of the δ18O variability • Opposite-sign correlations between δ18O and moisture picked from proximal or distal regions • No relationship between the precipitation deuterium excess and moisture source [ABSTRACT FROM AUTHOR]

Aerosol samples PM2.5 (44 filters), collected in 2013-2014 on the coast of the White Sea, were examined for the presence of trace elements. The entire sampling period was divided into conventional seasons: one snow-covered season, when the effect of terrigenous dust is minimal, and two snow-free seasons, when the effects of both anthropogenic and terrigenous sources are distinctly manifested. The snow-free seasons are characterized by the largest dispersion of elemental concentrations. The snow-covered season differs from snow-free seasons by the predominance of the western directions of air mass transport. Analysis of the directions of transport of air masses and aerosol admixtures to the observation site made it possible to identify a few groups of trace elements of natural (La, Nd, Sr, Ga) and predominantly anthropogenic origin (V, Ni, Cu and Pb, Bi, Cd). [ABSTRACT FROM AUTHOR]

On the basis of observational data on daily mean surface air temperature (SAT) and sea ice concentration (SIC) in the Barents Sea (BS), the characteristics of strong positive and negative winter SAT anomalies in Moscow have been studied in comparison with BS SIC data obtained in 1949-2016. An analysis of surface backward trajectories of air-particle motions has revealed the most probable paths of both cold and warm air invasions into Moscow and located regions that mostly affect strong winter SAT anomalies in Moscow. Atmospheric circulation anomalies that cause strong winter SAT anomalies in Moscow have been revealed. Changes in the ways of both cold and warm air invasions have been found, as well as an increase in the frequency of blocking anticyclones in 2005-2016 when compared to 1970-1999. The results suggest that a winter SIC decrease in the BS in 2005-2016 affects strong winter SAT anomalies in Moscow due to an increase in the frequency of occurrence of blocking anticyclones to the south of and over the BS. [ABSTRACT FROM AUTHOR]

Given its proximity to northern Africa, southern Spain is regularly affected by high-altitude African intrusions. This determines a well-defined wind dynamics at surface levels. Although this weather event—mainly recorded in spring and summer—coincides with the flowering season of many wind pollinated species, its potential influence on long term airborne pollen transport has been not investigated in detail. We analyse their influence on olive pollen transport at surface level in south Spain. Daily and bi-hourly olive pollen data from 2010 to 2015, recorded at two sites 150 km apart, Málaga (coast) and Córdoba (inland), were analysed together with 1) air masses at 300 m above ground level (m.a.g.l.), 2) surface wind direction and 3) surface wind speed over the same period. Air masses at 3000 m.a.g.l. were used to identify the periods under the influence of African intrusions. The combined analysis has enabled the identification of different pollen patterns and source contributions. In Málaga, hourly pollen peaks were recorded during the early morning coinciding with the arrival of north-westerly winds (developing sea-land breezes), with a minimal impact of local pollen sources; in Córdoba, by contrast, pollen concentrations reflected the joint contribution of local and long term sources, being the maximum concentrations associated with the arrival of southerly air masses in the afternoon. These results help to understand the potential distant sources and back-trajectories of olive pollen detected. In our case pollen from sources located at the west-northwest areas in the case of Malaga, and from the south in Cordoba. These results reinforce the idea that combined studies between synoptic meteorological and aerobiological data together with different atmospheric height air masses data, offer us a better explanation and understanding of the behaviour and the potential sources of recorded airborne data in a given place. [ABSTRACT FROM AUTHOR]

In this paper, we report the climatology of tropospheric ozone (O 3 ) and sub-micron aerosol scattering at the Mt. Bachelor Observatory (MBO, 2.8 km asl) in central Oregon, USA, during 2004–2015. The seasonal cycle for O 3 showed a bimodal pattern with peaks in April and July, while aerosol scattering ( σ sp ) was lognormally distributed with a very high peak in August and a smaller peak in May. The mean O 3 concentrations showed positive and significant trends in all seasons except winter, with a slope of 0.6–0.8 ppbv yr −1 . Monthly criteria for isolating free tropospheric (FT) and boundary layer influenced (BLI) air masses at MBO were obtained based on comparison of MBO water vapor (WV) distributions to those of Salem (SLE) and Medford (MFR), Oregon, at equivalent pressure level. In all seasons, FT O 3 was, on average, higher than BLI O 3 , but the seasonal patterns were rather similar. For σ sp the FT mean in spring was higher, but the BLI mean in summer was significantly higher, indicating the importance of regional wildfire smoke. To better understand the causes for the seasonal and interannual trends at MBO, we identified four major categories of air masses that impact O 3 , carbon monoxide (CO) and aerosols: upper troposphere and lower stratosphere (UTLS) O 3 intrusion, Asian long-range transport (ALRT), Arctic air pollution (AAP) and plumes from the Pacific Northwest region (PNW). ALRT and PNW plumes can be further divided into wildfires (WF), industrial pollution (IP) and mineral dust (MD). Over the 12 years of observations, 177 individual plume events have been identified. Enhancement ratios (ERs) and Ångström exponents (AEs) of aerosols were calculated for all events. The lowest slope of Δ σ sp /ΔO 3 is a unique feature of UTLS events. PNW-WF events have the highest averages for Δ σ sp /ΔCO, Δ σ sp /ΔO 3 and Δ σ sp /ΔNO y compared to other events. These ERs decrease during long-range transport due to the shorter residence time of aerosols compared to the other pollutants. ALRT-WF events have lower absorption AEs ( Å ap ) than PNW-WF, implying that brown carbon (BrC) is generated from biomass burning but its fraction decreases during long-range transport. Signatures of ERs and AEs are useful tools to identify different plume categories. These results demonstrate the increasing impact of baseline O 3 on US air quality due to both global sources and regional wildfire events. [ABSTRACT FROM AUTHOR]

Passive air samplers were used to evaluate long-term trends and spatial distribution of trace organic compounds in Antarctica. Duplicate PUF disk samplers were deployed at six automatic weather stations in the coastal area of the Ross sea (East Antarctica), between December 2010 and January 2011, during the XXVI Italian Scientific Research Expedition. Among the investigated persistent organic compounds, Hexachlorobenzene was the most abundant, with air concentrations ranging from 0.8 to 50 pg m −3 . In general, the following decreasing concentration order was found for the air samples analyzed: HCB > PeCB > PCBs > DDTs > HCHs. While HCB concentrations were in the same range as those reported in the atmosphere of other Antarctic sampling areas and did not show a decline, HCHs and DDTs levels were lower or similar to those determined one or two decades ago. In general, the very low concentrations reflected the pristine state of the East Antarctica air. Backward trajectories indicated the prevalence of air masses coming from the Antarctic continent. Local contamination and volatilization from ice were suggested as potential sources for the presence of persistent organic pollutants in the atmosphere. [ABSTRACT FROM AUTHOR]

In this paper, is presented a method for estimation of the effect of the transport process to aerosol optical properties. Aerosol optical data retrieved by lidars and sun-photometer measurements, are applied to Saharan dust events observed simultaneously at the two EARLINET/AERONET sites of Barcelona and Granada during the periods of June–September of 2012 and 2013. For this purpose, elastic lidar profiles and sun-photometer columnar retrievals are analyzed together with satellite observations and dust forecast models. Granada presents more than twice Saharan dust outbreaks compared to Barcelona. The scenarios favoring the Saharan dust outbreaks are identified in both places. The mineral dust originating in the Sahara region and arriving at both stations is usually transport wither over the Atlas Mountains or through an Atlantic pathway. Analyses of dust events affecting both stations reveal how differences in the transport process lead to differences in the aerosol optical properties measured at each station. Mean dust related Ångström exponent is 1.8 times higher in Barcelona than in Granada. This difference is a result of the additional contribution of anthropogenic aerosol, mainly in the aerosol fine mode, during the transport of the mineral dust plume over the Iberian Peninsula. [ABSTRACT FROM AUTHOR]

This study measured the concentrations of particulates and metallic elements in ambient air by using PS-1 sampler (TSP) at Longjing area. And this study focuses on the collection of ambient air particulates, metallic elements, particulate-bound mercury Hg(p), concentrations. In addition, the sources of ambient pollutants by way of back trajectory analysis are found. Moreover, test mean concentration variance differences for metallic elements (PM, Hg(p), Mn, Fe, Zn, Cr, Cu, and Pb) among the four seasons (spring, summer, autumn and winter) through ANOVA are calculated. The result indicates that the average highest particulate concentration occurred in winter season, and the order was winter > spring > autumn > summer, and the mostly highest average metallic element (Mn, Fe, Zn, Cr, Cu, Pb) concentrations occurred in autumn. Moreover, the mostly average lowest metallic element concentrations occurred in summer. In addition, the above results of backward trajectories that the major particulate pollutants parcel mainly come from northeastern Taiwan. Moreover, when comparing the results of the first half year to that of the second half year, the they indicated that all metallic elements displayed significant differences in concentrations except those of Hg(p), Mn, Fe, Zn. Finally, metallic element Hg(p) is the only one which showed no significant concentration difference from either seasonal variations or half-year observations. [ABSTRACT FROM AUTHOR]

Summertime atmospheric dynamics in the coastal zone of the industrialized Dunkerque agglomeration in northern France was characterized by a cluster analysis of back trajectories in the context of pollution transport. The MESO-NH atmospheric model was used to simulate the local dynamics at multiple scales with horizontal resolution down to 500 m, and for the online calculation of the Lagrangian backward trajectories with 30-min temporal resolution. Airmass transport was performed along six principal pathways obtained by the weighted k-means clustering technique. Four of these centroids corresponded to a range of wind speeds over the English Channel: two for wind directions from the north-east and two from the south-west. Another pathway corresponded to a south-westerly continental transport. The backward trajectories of the largest and most dispersed sixth cluster contained low wind speeds, including sea-breeze circulations. Based on analyses of meteorological data and pollution measurements, the principal atmospheric pathways were related to local air-contamination events. Continuous air quality and meteorological data were collected during the Benzene-Toluene-Ethylbenzene-Xylene 2006 campaign. The sites of the pollution measurements served as the endpoints for the backward trajectories. Pollutant transport pathways corresponding to the highest air contamination were defined. [ABSTRACT FROM AUTHOR]

Continuous sampling of aerosols is carried out on the north-western (NW) coast of the Kandalaksha Bay of the White Sea. Aerosol matter from 30 filters collected in summer and autumn, 2013, and spring, 2014, was studied by scanning electron microscopy. The elemental composition of aerosol matter was determined by the inductively-coupled plasma mass-spectrometry (ICP-MS). The major portion of aerosol particles collected in summer is of biogenic origin. Heavy metal concentrations in aerosols are at the Arctic background level. The distribution of trace element concentrations is characterized by simultaneous peaks of different elements. The backward trajectory analysis shows an increase in Ni and Cu concentrations corresponding to the arrival of air masses from the western part of the Kola Peninsula. That suggests the influence of smelters. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to identify the drivers responsible for the high particulate matter concentrations observed in recent years in several urban areas in Poland. The problem was investigated using air quality and meteorological data from routine monitoring network, air mass back trajectories and multivariate statistical modelling. Air pollution in central and southern part of the country was analysed and compared with this in northern-eastern 'The Green Lungs of Poland' region. The analysis showed that in all investigated locations, there is a clear annual cycle of observed concentrations, closely following temperature-heating cycles, with the highest concentrations noted in January. However, the main drivers differ along the country, being either connected with regional background pollution (in the central part of the country) or with local emission sources (in the southern part). The occurrence of high PM concentrations is most commonly associated with the influence of high-pressure systems that brought extremely cold and stable air masses form East or South of Europe. During analysed episodes, industrial point sources had the biggest (up to 70-80 %) share in PM levels on the days with maximum PM pollution, while remote and residential/traffic sources determined the air quality in the early stages of the episodes. Principal component analysis (PCA) shows that secondary inorganic aerosols account for long-range transported pollution, As, Cd, Pb and Zn for industrial point sources, while Cr and Cu for residential and traffic sources of PM, respectively. [ABSTRACT FROM AUTHOR]

Long-distance pollen transport can substantially raise local pollen levels, but their relative contribution has not yet been quantified temporally or spatially in ragweed infested regions. Using common ragweed ( Ambrosia artemisiifolia ) pollen accumulation at a ragweed infested area, Szeged, Hungary as a test case, this study attempted to: (1) identify, using cluster analysis, biogeographical regions that contribute to long-range transport of ragweed pollen to Szeged; (2) quantify the relative contribution of ragweed pollen from these regions; (3) determine the relative contribution of “local” and “transported” pollen for Szeged. Using the HYSPLIT model, three-dimensional backward trajectories were produced daily over a 5-year period, 2009–2013 for ragweed pollen accumulation at Szeged. A k -means clustering algorithm using the Mahalanobis distance was applied in order to develop trajectory types. Nine back-trajectory clusters were identified. Cluster 1 (direction: from the Channel area south of Great Britain) and cluster 5 (direction: from Northern Mediterranean) were found the most relevant potential long-distance sources for Ambrosia pollen transport to Szeged. Potential source contribution function ( PSCF ) and concentration weighted trajectory ( CWT ) values indicated additional potential source areas including the central and eastern part of France, the northern part of Italy and the Carpathian Basin. For Szeged on non-rainy days, medium-range transport is important, while on rainy days the two transport ranges have equal weights. Based on the Granger causality, annual pollen amount transported by the atmospheric circulation is 27.8% of the annual total pollen at Szeged. From this quantity, 7.5% is added to (due to transport), while 20.3% is subtracted from (e.g. because of wash-out by frontal rainfalls going towards Szeged) local sources. [ABSTRACT FROM AUTHOR]

Continuous methane (CH 4 ) concentrations were measured in Northern Spain over two years (2011–2012) by multi-point sampling at 1.8, 3.7 and 8.3 m using a Picarro analyser. The technique is based on cavity ring-down spectroscopy. The contrast in mean concentrations was about 1.2 ppb, with 95th percentiles differing by 2.2 ppb and mean minimum concentrations proving similar. Temporal variations of CH 4 were also analysed, with a similar seasonal variability being found for the three heights. The highest CH 4 concentrations were obtained in late autumn and winter and the lowest in summer, yielding a range of 52 ppb. This variation may depend on the active photochemical reaction with OH radical during a period of intense solar radiation and changes in soil conditions together with variations in emissions. Peak concentration levels were recorded at night-time, between 5:00–7:00 GMT, with mean values ranging between 1920 and 1923 ppb. The lowest value, around 1884 ppb, was obtained at 16:00 GMT. This diurnal variation was mainly related to vertical mixing and photochemistry. Therefore, CH 4 concentrations were also examined using the bulk Richardson number (R B ) as a stability indicator. Four groups were distinguished: unstable cases, situations with pure shear flow, transitional stages and drainage flows. The highest contrast in mean CH 4 concentrations between lower and upper heights was obtained for the transition and drainage cases, mainly associated to high concentrations from nearby sources. The impact of long range transport was analysed by means of 3-day isobaric backward air mass trajectories, which were calculated taking into account origins from Europe, Africa, the Atlantic Ocean and Local conditions. Assessment of the results showed the influence of S and SE wind sectors, especially with Local conditions associated with low winds. Finally, an estimation of the background CH 4 concentration in the study period provided an average value of about 1892 ppb. [ABSTRACT FROM AUTHOR]

This study presents the results about the influence of the weather elements on the Cloud Condensation Nuclei (CCN) size distribution. For this purpose the data for summer (July) and winter (December) conditions of 2016 from the highest in the Balkan Peninsula Environmental Observatory on Mt. Moussala are used for finding the extrema of the CCN concentrations. To characterize the synoptic situation we extend our study with data for the geopotential height, wind and temperature at 700 hPa for the considered two months. We use the HYSPLIT model of the National Oceanic and Atmospheric Administration to trace the backward trajectories of the air masses for the previous 72 h before their arrival at Mt. Moussala. Thus we identify two major types of trajectories, sea and continental, depending on the time spent over the corresponding surface and three groups according to the predominant height, from the lowest to the highest one. The prevailing trajectory type in the two months studied is the continental one. During most of July the air masses are coming along the high layers of the atmosphere, while in December the majority of the trajectories are coming from the lowest layers. We match these two types of trajectories with an existing synoptic classification scheme of the weather patterns over the Balkan region. • The CCN number concentrations are much higher in July than those in December. • Three basic CCN sizes (from all 20 sizes) are distinguished. • The total number of CCN rescales the size distributions to a universal form. • The synoptic situations are clarified for the days with optimal of the CCN number. • The continental backward trajectories of air masses prevail in both months. [ABSTRACT FROM AUTHOR]

A new classification method of the large-scale circulation characteristic for a specific target area (NW Iberian Peninsula) is presented, based on the analysis of 90-h backward trajectories arriving in this area calculated with the 3-D Lagrangian particle dispersion model FLEXPART. A cluster analysis is applied to separate the backward trajectories in up to five representative air streams for each day. Specific measures are then used to characterise the distinct air streams (e.g., curvature of the trajectories, cyclonic or anticyclonic flow, moisture evolution, origin and length of the trajectories). The robustness of the presented method is demonstrated in comparison with the Eulerian Lamb weather type classification.A case study of the 2003 heatwave is discussed in terms of the new Lagrangian circulation and the Lamb weather type classifications. It is shown that the new classification method adds valuable information about the pertinent meteorological conditions, which are missing in an Eulerian approach. The new method is climatologically evaluated for the five-year time period from December 1999 to November 2004. The ability of the method to capture the inter-seasonal circulation variability in the target region is shown. Furthermore, the multi-dimensional character of the classification is shortly discussed, in particular with respect to inter-seasonal differences. Finally, the relationship between the new Lagrangian classification and the precipitation in the target area is studied.

In this study, 24-hour backward trajectories of the air mass in Nanjing were calculated by using the HYSPLIT model with the NCEP global reanalysis data from March 2019 to February 2020. The backward trajectories combined with the hourly concentration data of PM 2.5 were then utilized in the trajectory clustering analysis and potential pollution source analysis. The results showed that the average concentration of PM 2.5 in Nanjing was(36±20) μg·m -3 during the study period, with 17 days exceeding the grade Ⅱ national ambient air quality standards (75 μg·m -3 ). PM 2.5 concentration exhibited clear seasonal variation, with winter (49 μg·m -3 )>spring (42 μg·m -3 )>autumn (31 μg·m -3 )>summer (24 μg·m -3 ). PM 2.5 concentration was significantly positively correlated with surface air pressure but significantly negatively correlated with air temperature, relative humidity, precipitation, and wind speed. Based on the trajectories, seven transport routes were identified in spring, and six routes for the other seasons. The northwest and south-southeast routes in spring, southeast route in autumn, and southwest route in winter were the main pollution transport routes in each season, with the characteristics of short transport distance and slow air mass movement, indicating that local accumulation was one of the main reasons for the high value of PM 2.5 in quiet and stable weather. The distance of the northwest route in winter was large, and the PM 2.5 concentration was 58 μg·m -3 , which was the 2 nd highest concentration in all routes, indicating that the cities in the northeast of Anhui had a great transport influence on Nanjing PM 2.5 . The distribution of PSCF and CWT was relatively consistent, and the main potential source areas were mainly local and adjacent areas of Nanjing, indicating that PM 2.5 control is needed to strengthen local control and carry out joint prevention and control with adjacent areas. Winter was most affected by transport, its main potential source area was located at the junction of northwest Nanjing and Chuzhou, and the main source origin was in Chuzhou; therefore joint prevention and control should be expanded to Anhui.

Air masses reaching the Iberian Peninsula, which is located between two continents and two seas, have been classified. 24-h backward air trajectories were calculated each hour for three years using the METEX model at a site in the centre of the northern plateau of the Iberian Peninsula where the air flow has scarcely been investigated to date. Rather than the usual Euclidean geometry, spherical trigonometry, together with the kernel regression method, was considered to calculate trajectory distances to the site. Numerical indicators allow for an accurate description of the results. Ranges surrounding the site from E to S evidenced a restriction in the movement of the arriving flow. However, the range to the N showed only a slight effect. A noticeable seasonal contrast was observed between winter, whose distances were the greatest, and summer, which displayed the shortest distances. Trajectory clusters, initially not considered in the METEX model, were obtained with different metrics to determine the air mass pathways reaching the site. Five clusters of trajectories were selected so as to easily explain the directions and distances covered. Regional and long range transport were observed in clusters from the NE, NW and SW. The NE cluster presented an orographic deviation and local processes were limited to the SE cluster. Finally, seasonal analysis revealed singular behaviour during autumn, when local processes centred on the N–S direction. [ABSTRACT FROM AUTHOR]